Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The core baffle of a PWR is loaded by the pressure difference between bypass and core and by temperature profiles developing from gamma heating and heat transfer into the coolant. Strain, deformation and gaps between the sheets resulting from this load are determined con-sidering the effect of neutron irradiation induced creep of the core baffle bolts. The finite ele-ment code ANSYSÒ is applied for the thermal and mechanical analyses. The FE-model comprises a complete 45° sector of the core baffle structure including the core barrel, the formers, the core baffle sheets and about 230 bolt connections with non-linear contact between the single components and the effect of friction. The complete analysis requires three major steps:

1. Evaluation of the three dimensional distribution of neutron flux and gamma induced in-ternal heating with the Monte Carlo code MCNP®. These calculations are based on pin wise power distributions at the core edge for typical loading patterns.
2. Calculation of the temperature distribution in the core baffle for different operational conditions and core loading patterns, considering heat conduction in the components with internal heat sources (gamma heating, step 1) and convectional boundary condi-tions (heat transfer coefficients and bulk temperature of the coolant).
3. Calculation of time dependent deformation, stresses and strains taking into account weight, pressure loads, temperature fields for different load situations (step 2), prestress-ing, irradiation induced creep of the bolts as correlated to neutron flux (step 1).

The results show the equalizing effect of redistribution of bolt loads from high flux to lower flux exposure locations in a self controlled process, keeping the mechanical and geometrical stability of the core baffle structure and leaving the gaps between sheet edges unaffected.

The coupling of Bloch oscillations to longitudinal optical phonons is investigated in a narrow-well InGaAs/InAlAs superlattice. A strong increase of coherent phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with different optical phonon modes. The rapid dephasing of the Bloch oscillations due to field induced tunneling from the weakly bound miniband into above-barrier continuum states leads to an additional and new excitation process of coherent phonons in superlattices at high electric fields. Polarization dependent measurements confirm their generation via Coulomb interaction excluding any contribution through impulsively stimulated Raman scattering.

Since 1997 in-beam PET is successfully used to monitor the precision of dose application in highly conformal carbon ion tumour therapy at the experimental facility at the Gesellschaft f\"ur Schwerionenforschung Darmstadt (GSI), Germany.
The potential of the method for the monitoring of proton therapy is currently under investigation.
In our first experiment, three monoenergetic proton beams were stopped in targets of organic plastics placed in the centre of the field of view of the in-beam PET scanner at GSI. The beta^{+}-activity was found to be three times higher than that induced by carbon ions at the same range and applied dose. The reconstructed beta^{+}-activity distributions were rather well reproduced by model calculations. The possible extraction of valuable clinical information from the comparison between measured and calculated beta^{+}-activity distributions is discussed.
Despite the weaker spatial correlation between beta^{+}-activity and dose depth-profiles in the proton case, the presented analysis strongly supports the feasibility and clinical usefulness of in-beam PET for the monitoring of proton therapy.

A thin Si3N4 surface layer is formed by implantation of 60 keV 15N nitrogen ions into single-crystalline silicon <100> with a fluence of 5.6x1017 ions/cm2 and subsequent annealing (1295°C, 15 min) under high vacuum conditions. The 15N depth distribution is measured with the resonant nuclear reaction 15N(p,alpha-gamma)12C. The formation of Si-N bonds is proven by Fourier transform infrared spectroscopy using samples implanted with 14N ions and 15N ions, respectively. The crystallinity of the Si3N4 surface layer is studied by X-ray diffraction and transmission electron microscopy. The annealing process leads to the formation of a polycrystalline alpha-Si3N4 surface layer with a thickness of 90 nm. The analysis of high resolution TEM micrographs shows that the layer is split into two sublayers both consisting of single alpha-Si3N4 crystals with lateral extension up to 500 nm.

Obwohl zur Anwendung von Magnetfeldern bei der Erstarrung, z. B. beim Stranggießen von Al-Legierungen oder Stahl und bei der Kristallzüchtung, bereits Erkenntnisse vorliegen, befindet sich dieses Gebiet erst am Anfang seiner Entwicklung. Die Beeinflussung des Temperaturfeldes durch magnetfeldinduzierte Strömungen beim Phasenübergang flüssig/fest läßt wegen der Auswirkungen auf Keimbildungs- und - Kornwachstumsreaktionen ein bisher kaum beachtetes Entwicklungspotential für Werkstoffe und Technologien erwarten. Zielstellung der Arbeiten ist die Erzeugung eines feinkörnigen, globulitischen Gefüges bereits in Folge des Erstarrungsprozesses, analog dem, welches in Knetlegierungen nach einer Umformung und Wärmebehandlung vorliegt. Zu klären ist, inwieweit die bei herkömmlicher Erstarrung auftretenden Konzentrations- und Eigenschaftsgradienten sowie die Lunkerbildung unterdrückt werden können. Ferner soll untersucht werden, inwieweit durch die Dauer und Intensität magnetfeldinduzierter Strömungsvorgänge speziell im Zweiphasengebiet flüssig/fest Einfluß auf die Entstehung und den Aufbau des Endgefüges genommen werden kann.
Vorgestellt werden experimentelle Arbeiten zur Untersuchung der gerichteten Erstarrung von PbSn-Legierungen in einem rotierenden Magnetfeld. Gemessen werden Abkühlungskurven und Geschwindigkeitsmessungen während des Erstarrungsprozesses.

Due to significant differences in material properties such as density or surface tension the behaviour of gas bubbles reveals some peculiarities in liquid metal applications as compared with ordinary water flows. Moreover, questions about the wetting of solid surfaces or the role of impurities which have a minor importance in water systems, however, show a more dominant influence in metallic melts.
In view of the production of metallic foams the control of the properties of liquid metal two-phase flows by electromagnetic forces in a contactless way would be very attractive. Some examples of magnetic field applications will be presented with respect to the bubble generation process, the dispersion of gas bubbles or the momentum and heat transfer properties of liquid metal bubbly flows.
If gas bubbles are injected into a liquid metal characterised by a large surface tension one should take care to get a good wetting between the fluid and the surface of the gas injector. Otherwise, the gas would try to spread out along this interface to form gas layers. A control of the bubble size and formation rate becomes difficult. The comparison between experiment and theoretical models describing bubble formation processes requires an ideally wetted gas injector. The bubble formation in mercury and the eutectic alloy InGaSn has been studied by means of several methods of gas injection, for instance through single orifices or injectors made from sintered metals with a mean porosity of a few microns. X-ray measurements have been used to directly observe the resulting gas bubbles rising in the liquid metal. In the case of a single orifice the influence of electromagnetic forces on the bubble frequency has been demonstrated.
The transport properties of small argon bubbles have been studied in turbulent upwards channel flows of sodium and mercury. The bubbles were injected by a single orifice located in the centre of the channel cross section. After a distinct distance the local void fraction and the bubble velocity have been measured by means of electrical resistivity probes. The flow has been exposed to external magnetic fields directed transverse or longitudinal to the mean flow direction. Experimental results showing the effect of the magnetic field on the horizontal gas distribution and the ratio between gas and liquid velocity will be presented.
The variety of standard measuring techniques to characterise liquid metal flows is limited due to the nature of metallic melts. However, the availability of diagnostic methods to get information about the structure of liquid metal two-phase flows is a crucial point. A selection of measuring techniques which have been developed in our group to determine flow parameters such as the phase velocities, the void fraction or the bubble size will be discussed with respect to their capabilities and restrictions in various applications.

Constitutive models for the interaction between the gaseous and the liquid phase are needed for application of CFD codes on two-phase flow phenomena as they occur in many scenarios concerning safety analysis of nuclear reactor systems. For the bubble flow and slug flow regime this especially concerns the forces acting on a bubble in the liquid flow field and bubble coalescence and break-up. Vertical pipe flow is an appropriate situation to investigate these effects. This is done experimentally by using new measuring techniques, which allow measurements with a high resolution in space an time. The experimental results show, that besides local effects also the bubble size distribution has an important influence of the development of the flow. A simplified model was developed to test and improve the constitutive laws. To ensure the transferability of the models experiments for vertical pipes with an inner diameter of up to 200 mm are planned, using our new test facility TOPFLOW.

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Especially in Saxony and Thuringia the intense uranium mining and milling causes a wide variety of contaminated waters. These seepage and mine waters contain besides uranium several inorganic and organic complex forming agents [1, 2].
Heavy metals in the aquatic environment are normally transported as a complexed species. Knowledge about the complex formation is therefore an essential constituent in prediction of the migration of these elements.
Spectroscopic methods have the advantage to be non-invasive and non-destructive. The high intensity of laser light sources allows the excitation of all species in the illuminated volume. Therefore laser based methods reach low detection limits.
At higher concentrations uranium forms often poly-nuclear complexes. Therefore studies of the complex formation should be carried out at concentrations which are relevant to those of the contaminated sites. Also the direct determination of the species formed in the mining related waters is essential for the selection of effective cleaning methods.
As uranium(VI) shows fluorescence properties (except carbonate species) time-resolved laser-induced fluorescence spectroscopy enables the detection of species up to detection limits of 10-8 M. Besides the study of the complex formation (sulfate, phosphate, arsenate) we determined the formed species in several mining related waters as function of pH. The change in the speciation of uranium(VI) is shown to be in agreement with calculations, if also the formation of formerly unknown species is included.
Carbonate species are dominating the uranium(VI) speciation in the neutral pH range. As mentioned above these species do not emit fluorescence. Uranium(IV) does not show fluorescence properties. In these cases only the absorption spectra can be used for the direct determination of these species. However the concentration of uranium in the natural environment is much lower than the detection limit of conventional UV-VIS spectroscopy. Using laser-induced photoacoustic spectroscopy the detection limit can be decreased by about three orders of magnitude. Studies of the complex formation of uranium(IV) with phosphate and arsenate will be presented [3], demonstrating the advantage of direct speciation methods.

[1] G. Geipel, G. Bernhard, M. Rutsch, V. Brendler, H. Nitsche; Speciation in Water Released from Mining and Milling Facilities In T.E. Baca and T. Florkowski (eds.), The environmental Challenges of Nuclear Disarmament, Kluwer Academic Publishers, 2000, p. 323-332
[2] G. Bernhard, G. Geipel, V. Brendler, H. Nitsche; Speciation of Uranium in Seepage Waters from a Mine Tailing Pile Studied by Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS); Radiochimica Acta, 74, 87, (1996)

The nuclear microprobe at the 5 MV tandem accelerator of the Central Institute for Nuclear Research at Rossendorf is realized by object diaphragms of 50, 70 and
100-mu-m and a magnetic quadrupole triplet. The proton microbeam with a spot size of about 4-mu-m is used for NRA. Depth profiles for oxygen in zirconium
alloys and for fluorine in human teeth were measured by scanning the beam linearly over cross sections of the samples using the resonant proton backscattering at 4.5
MeV and the nuclear reaction F-19(p, alpha(0))O-16 at 3 MeV, respectively.

For studying deuterium depth profiles in surfaces of JET (Joint European Torus) limiters, a new deuterium profiling method was developed and used. A smooth
10-degrees slope plane on the specimen was produced by ion beam slope cutting using a 10 keV Kr ion beam. To detect deuterium the nuclear reaction H-2(C-12,
p)C-13 was used at E(C-12(3+) = 7.5 MeV. The very narrow proton peak could be clearly separated from the background of the spectra. For measuring the
lateral and vertical deuterium distribution the C-12 beam of the Rossendorf 5 MV tandem accelerator was focussed to about 6-mu-m and scanned across the
specimen. The preliminary results show a deuterium distribution up to a depth of about 5-mu-m in a carbon limiter

The fluorine concentration of chemically enriched hydroxylapatite (Ca10(PO4)6(OH)2) was measured by means of PIGE using the nuclear reactions F-19(p, p'
gamma)F-19 and F-19(p, alpha-gamma)O-16. The experiments were done in-two runs with 1.68 and 2.15 MeV proton incidence. The results determined with
inelastic scattering are in good agreement in the two runs. The samples are suitable as new fluorine standards in the ppm region to study the fluorine content in tooth
enamel.

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For measuring hydrogen concentrations up to a depth of several tens of micrometers we propose the use of a special sample preparation method - ion beam slope
cutting. The principle and the experimental arrangement are described. The depth profiles are obtained by line scans of the nuclear microbeam over the slope planes.
The nuclear reactions (H(15N, alpha0)C)-H-1-C-12 and (H(B, alpha)2alpha)-H-1-B-11 were investigated and proved suitable for hydrogen analysis with the
microbeam detecting the alpha-particles at backward angles.

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SiO(x)N(y) layers in the thickness range from 4 to 20 nm are grown by rapid thermal processing (RTP) using NH3 and N2O as nitridants. I-V measurements,
investigation of the time-dependent breakdown, and post-stress C-V display significant distinctions between the layers according to their growth conditions. For the
explanation of the electrical behaviour, the compositional structure was examined by means of AES, SIMS, and NRA.

Bone structures, represented in the form of so-called lines of arrested growth, were observed in medieval human femur. Because process and causes of line
formation are not yet understood multielement analysis on a cross section of a femoral bone was carried out by micro PIXE using the Rossendorf nuclear
microprobe. A series of line profiles across the bone lines, elemental maps and point analyses on a line and beside it show reproducibly increased concentrations of
the trace elements Mn, Fe, Zn, Pb and Sr on the bone lines.

Siliconoxynitride layers with thicknesses between 5 and 10 nm were grown on (100) oriented silicon by rapid thermal processing (RTP) using either N20 or NH3 as nitridant. In order to study the trapping behaviour at the interface and in die insulator bulk, capacitance-voltage (CV) and current-voltage (IV) measurements have been performed combined with different magnitudes of Fowler-Nordheim stress. In addition, Deep Level Transient Spectroscopy (DLTS) has been applied for interface state detection. Auger Electron Spectroscopy (AES) has been used to obtain depth profiles for Si, N, 0 and C. The deconvolution of die AES signal displays significant peak contributions related to intermedium oxidation states. Nuclear Reaction Analysis (NRA) was successfully applied for hydrogen detection in buried SiOXNY thin films.

Titanium oxides are considered as blood compatible surfaces, however, it may be possible to improve the compatibility to the inner lining cells of blood vessels by addition of Ag which modifies the electronic properties of this oxide. Therefore, Ti–Ag–O films with the thickness of 200–350 nm have been deposited on Si substrates using an ion beam assisted deposition (IBAD) system which has two evaporators to allow a simultaneous deposition of Ti and Ag. The evaporation rates of Ti and Ag, as well as the flow rate of O2 have varied. For physicochemical analysis of the films, glancing incidence X-ray diffraction (GIXRD) analysis, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were performed. The formed phases in Ti–Ag–O films consist of TiO2, AgO, Ag2O, Ag, TiAg, AgTi3, and low valent titanium oxides. The bovine aortic endothelial cell line GM07373 was grown on these surfaces in a medium with 10% fetal bovine serum. The toxicity of the layers was rated by the release of lactate dehydrogenase (LDH) from the cells and are found to be below the detection limit; the cell adhesion was investigated by fluorescent staining of the adhesion molecule vinculin and the cytoskeleton protein filamentary actin; the cell nuclei were counterstained with DAPI, showing good cell adherence, good compatibility to endothelial cells, and no indication of apoptotic cell death.

Three effects have been observed in wet-thermally grown SiO2/Si structures under bombardement with energetic N-15 ions:

(1) Out-diffusion of H from the SiO2/Si system through the surface,
(2) Accumulation of H at the SiO2/Si interface,
(3) Changes in the optical fingerprint spectra of Psi and Delta in dependence on lambda (wavelength) obtained by ellipsometric measurements.

The coolant mixing is significant for safety assessment of boron dilution and cold water transients. For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM was constructed. ROCOM is a 1:5 scaled Plexiglas model of the PWR Konvoi disposing of four loops with fully controllable coolant pumps. Mixing of both overcooled and de-borated water is investigated by adding a tracer salt solution, performing conductivity measurements by wire mesh sensors and velocity measurements by the LDA technique. The tracer concentration fields established by coolant mixing under steady-state and transient flow conditions were investigated. The experiments aimed at the validation of CFD codes. CFD calculations were carried out with the code CFX-4. In case of running pumps, ROCOM measurements provided a tracer concentration maximum in the core sector below the inlet nozzle of the loop with tracer injection, while the maximum reaches more than 90% of the simulated overcooling in the corresponding loop. This situation is typical for a cold water transient due to main steam line break. During start-up of the first pump being relevant for boron dilution transients, the maximum of the tracer concentration appears at the core inlet at positions opposite of the loop with injection, while the maximum boron dilution strongly depends on slug size, slug initial position and mass flow ramp. A good agreement was achieved between measuring results and CFD calculations.

A semi-analytical perturbation reconstruction model (SAPR) has been developed allowing the description of the coolant mixing inside the reactor pressure vessel of PWRs by superposition of response functions on nearly Dirac-shaped perturbations, which can be determined experimentally or from CFD calculations. SAPR provides realistic time-dependent boron concentration fields at the core inlet for the analysis of a hypothetical boron dilution event after start-up of the first main coolant pump in a generic four-loop PWR. Core calculations were performed with the 3D reactor dynamics code DYN3D. By varying the initial slug volume it was found, that for the given core loading pattern slugs of less than 20 m3 do not lead to re-criticality of the shut-off reactor. Calculations with the bounding slug volume of 36 m3 show, that the corresponding reactivity insertion does not result in core damage.

In the Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, electrode-mesh sensors were developed, which allow the measurement of the electrical conductivity distribution in a flow duct with a rate of up to 10 000 frames per second. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Beside a description of the working principle, this lecture focuses on different applications of the method, which will be illustrated by digital image sequences obtained by electrode-mesh sensors.
The sensor consists of two planes of wire grids placed into the flow in a short distance behind each other. The angle between the wires of both grids is 90 deg. The wires of the first plane (transmitter plane) are supplied with pulses of a driving voltage. During the measuring cycle, they are activated by a multiplex circuit in a successive order. After an analogue/digital conversion the receiver signals are recorded by a data acquisition computer connected to AD converters and stored for each receiver electrode separately. This procedure is repeated for all transmitter electrodes. In this way the distribution of the electrical conductivity over the cross section occupied by the sensor is obtained row by row. This data is used for slow-motion visualization of transient flows and for quantitative measurements of gas fractions and their profiles, bubble sizes and velocities.
Special attention was given to achieve a DC free excitation of the electrodes in order to suppress the imaginary part of the measured impedance. Measures were taken to suppress cross-talk between parallel electrodes. The first generation device allowed measurements in a grid of 16 x 16 measuring points distributed over the cross section of the flow duct with a rate of 1200 frames per second.
The high spatial and time resolution of the wire-mesh sensor allows to calculate bubble size distributions from the sequence of frames. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. After assigning the local instantaneous gas fractions (pixels) to bubbles by a bubble recognition algorithm, the volume of each identified bubble is obtained by adding the local values belonging to the selected bubble. Capabilities and accuracy of this method were investigated using a sensor, which was built into a transparent perspex channel. Combined visualizations using the frames of a high-speed video camera together with the measuring sequences of the wire-mesh sensor have shown that the sensor acts as a bubble fragmenting obstacle. It could nevertheless be proven, that the sensor signal represents the bubble geometry present in the upstream flow, i.e. before the disturbance, with a good accuracy.
In the first application the sensor was used to study the evolution of the flow pattern in an upwards air-water flow. The visualization shows the result of an air injection through wall orifices of 4 mm diameter (pipe diameter 51.2 mm) and the evolution of the flow pattern from L/D = 0.6 to L/D = 60. Large primary bubbles are observed, which are both coalescing and fragmenting in the direction of the flow. Large bubbles tend to travel towards the center of the pipe. At the end of the test section a slug flow is established. Another wire-mesh sensor was used by the University of Munich, Germany, to visualize the effect of a globe valve to the flow regime in a horizontal pipe. The image sequence shows the initial slug flow through the open globe valve and the transition of the flow pattern during closing of the glob valve.
Beside air-water flows the sensor can also be applied to measure the void fraction in steam-water mixtures. The sensor is used to study natural circulation instabilities in a boiling water reactors. For this purpose, two wire-mesh sensors are installed at the CIRCUS test facility of the U...

Damages in pipeline systems are often ascribed to water hammer and cavitational hammer. The resulting leakage can cause considerable damages to mankind and environment. To control these pressure surges, Fraunhofer UMSICHT and Forschungszentrum Rossendorf have conducted experiments whose results are used to develop new methods for the prevention of water hammer and cavitational hammer. The fast-acting valve is equipped with an innovative hydraulic braking system ("ABS-Armatur") and is combined with a check valve to suppress the water hammer. Since the described system does not need any additional energy source and adapts automatically to changes of the pipe system parameters, it is also regarded as particularily suitable for already existing plants.

High-spin states in ¹²³Xe were populated in the
¹¹⁰Pd(¹⁸O,5n)
reaction at 75 MeV and gamma-ray coincidences were measured with
the GASP spectrometer.
A new rotational sequence of enhanced dipole transitions was established.
This band, as well as a similar band in ¹²⁴Xe, may be described
within the framework of the tilted axis cranking model as bands for
which comparable amounts of angular momentum are generated by
magnetic and collective rotation, respectively.

Thin films of Ba3Ca1.18Nb1.82O8.73, prepared in a sol-gel process by multiple dip-coating on silicon wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressure and temperature. The hydrogen content was determined ex situ at room temperature using nuclear resonance reaction analysis. From the resulting water vapour pressure-composition isotherms the absorption enthalpies Delta(empty set)H(o), Delta(empty set)H(t) and the absorption entropy Delta(empty set)S were calculated, using a two-site model, based on Fermi-Dirac statistics. On Ba3Ca1.18Nb1.82O8.73 bulk material also impedance spectroscopy, concentration and fuel-cell measurements as well as neutron diffraction were performed. From these data, taken together, the proton diffusion coefficient D-H could be evaluated and compared to quasielastic neutron scattering results.

The nucleus ⁷⁰Se was studied using the ⁴⁰Ca(⁴⁰Ca, 2α) reaction at a beam energy of 185 MeV. Gamma rays were measured with the EUROBALL III spectrometer. The known positive-parity bands have been extended and one new band of positive parity and two of negative parity have been identified.
These bands are interpreted in terms of the cranked Nilsson-Strutinsky approach. Calculations suggest that the two negative-parity bands, which have the same signature, are both based on a configuration with two protons and three neutrons lifted from the fp shell to the g _9/2 orbital, but at different nuclear shapes. This represents a shape coexistence at high spin.

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Deuterium inventories have been measured in plasma facing components of ASDEX Upgrade. Nearly 60% of the total D-inventory was observed in the lower inner divertor target plate in redeposited layers of low-Z material. The outer divertor, however, was found to be dominated by erosion processes and correspondingly retained a much lower amount of deuterium. The D-inventory at the main chamber plasma facing components can be explained by a model employing implantation of charge-exchange neutrals, which yields very good agreement with the experimental findings for all surfaces not exposed to direct ion fluxes.

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Raman spectroscopy, spreading resistance probe (SRP) analysis, scanning electron microscopy (SEM) and elastic recoil detection analysis (ERDA) studies were carried out on H-plasma treated and annealed p-type Czochralski (Cz) Si. The formation of voids filled with hydrogen molecules was observed by Raman spectroscopy after plasma hydrogenation. The Raman and ERDA measurements show that molecular hydrogen can be released from nanovoids at 600 °C which leads to the formation of empty voids. ERDA and SEM investigations show that after the hydrogen plasma treatment the formation of voids filled by hydrogen occurs at a depth of about 400 nm. SRP measurements show, that at 400 °C post-hydrogenation annealing for 10-60 min a fast diffusion of hydrogen into the bulk occurs. This leads to the hydrogen enhanced thermal donor formation and therefore to a carrier profiles modification up to a depth of a few hundred microns. The Raman measurements show that the molecular hydrogen can not be released from nanovoids at 400°C which is in good agreement with ERDA data. Our investigations give a method for the low-temperature, low-cost modification of die Cz Si substrates which leads to die formation of a carrier gradient in die bulk, to surface structuring and to voids formation in the subsurface region.

A Distributed Electron Cyclotron Resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit ta-C:H (Diamond-Like Carbon, DLC) thin films at RT. A graphite sputtering target immersed in an argon plasma was used as carbon source. The Ar plasma density was about 5 exp(10) cm-3. Single crystalSi substrates were RF biased to a negative voltage of -80 V. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H ---> 12C +4He + Gamma, elastic recoil detection analysis (ERDA) and Rutherford backscattering (RBS) were used to investigate the early phase of the growth. The morphology of the films grown at low pressure (0.3 mTorr) is shown to be dominated by stress-mediated nucleation leading to formation of basket-like clusters of circular hillocks 20 nm high surrounded by a planar, mostly sp2 bonded film ~8 nm thick. With increasing plasma pressure the spatial frequency of the hillocks becomes random and the growth is dominated by the Stranski-Krastanov mode. The XPS data taken at decreasing emergence angles show that the structure of the hillocks is dominated by sp3 bonded carbon. The XPS argon signal disappears at 10° emergence angle indicating that integration of argon occurs mainly within the sp2 bonded regions. The NRA and ERDA analysis show that the amount of integrated hydrogen decreases with increasing substrate current density. RBS data indicate that increasing bias enhances argon integration.

A distributed electron cyclotron resonance (DECR) plasma reactor powered by a microwave generator operating at 2.45 GHz (800 W) was used to deposit (t)a-C:H thin films at RT on <100> Si substrates RF biased within the range 25 < |Vo| < 600 V. C2H2 was used as precursor. The plasma pressure was varied within the range 0. 1 < P < 1 .5 mTorr. The films were analysed using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. The hydrogen content NH and the density of the films were determined from nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H ---> 12C + 4He + Gamma. Positron annihilation spectroscopy was used to detect the porosity. The evolutions of NH as a function of the substrate ion current density n+ and as a function of Vo show that the hydrogen incorporation results from the competition between chemisorption and deposited energy density related effects. The increase of the hydrogen incorporation leads to a decrease in the film density and a lower deposition rate. The porosity of the films deposited at low pressure (~ 0. 1 mTorr) with Vo = - 80 V has been detected. The comparison between results of SRIM-2000 simulations and the evolution of NH as a function of Vo shows that the porosity and the hydrogen content are not correlated. The absorption of oxygen and nitrogen for the low density films has been detected from the observation of the 3250-4000 cm-1 infrared (IR) band.

Until recently, the existence of oscillatory mean-field dynamos of the alpha^2-type with spherically symmetric and isotropic alpha was an open question. We find such dynamos by means of an evolutionary strategy, and we illustrate the spectral properties of the corresponding dynamo operators.

Alloying by high dose ion implantation of iron into magnesium and aluminum

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The encapsulation of active centres is a widespread principle used in biological systems. So, enzymes may wrap certain substrates leading to the complete shielding from the environment. Currently, dendrimers are considered to be applicable as artificial encapsulating systems which can effectively bind guest molecules. In principle, dendrimers can accommodate different kind of guests, such as anionic species, metal ions, and neutral substrates. Furthermore there is the possibility to graft biomolecules on the periphery of dendrimers, by which in particular the biodistribution can be influenced. These unique structural features and properties make dendrimers attractive as candidates for imaging and therapeutic purposes. In this nexus, the encapsulation of radionuclides by dendritic boxes^[1] (I) and the fixation by dendrons^[2] (II) seems to be promising concepts.

We report on preliminary results of binding pertechnetate and perrhenate by polypropyleneamine dendrimers. Lipophilic urea-containing dendrimers are efficient carriers for these anions. We could shown that the polyamine skeleton is suitable for binding some anions inside of the dendrimer.
The concept of dendritic encapsulation in view of the development of highly stable metallodendrimers is discussed. Some examples for potential copper- and rhenium-containing dendrimers are presented.

[1] J. F. G. A. Jansen, E. W. Meijer, E. M. M. de Brabander-van den Berg: The dendritic box: Shape-selective liberation of encapsulated guests, J. Am. Chem. Soc. 1995, 117, 4417-18.
[2] S. Hecht, J.M.J. Frechet: Dendritic encapsulation of function: Applying nature's site isolation principle from biomimetics to materials science, Angew. Chem. Int. Ed. Engl. 2001, 40, 74-91.

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Diamond-like carbon is a system of rather high disorder as it has a wide optical absorption tail and a high density of paramagnetic defects. The defect density
remains high even in DLCs containing 30-60% hydrogen, so hydrogen does not appear to passivate defects well unlike in a-Si:H. To investigate the role of hydrogen
on the disorder in DLCs we have investigated the effect of low concentrations of hydrogen on the disorder in ta-C, by introducing 10(-6)-10(-3) mbar hydrogen into
the deposition of ta-C by filtered cathodic vacuum are (FCVA), which corresponds to 0.1-15 at.% hydrogen in the films. Higher pressures of hydrogen reduces the
ionisation leading to sp(2) bonding, and ultimately the thermalisation of the plasma leads to nanotubes and fullerenes. The deposited ta-C:H films were investigated by
electron energy loss spectroscopy (EELS), Raman spectroscopy, optical measurements, electronic transport and N-15 resonant nuclear reaction analysis. Plasma
characterisation with a retarding field analyser showed that the ion current density remains nearly unchanged in the pressure range used to deposit the films. Raman
measurements indicate the onset of clustering of sp(2) sites when the hydrogen pressure exceeds 2 x 10(-4) mbar. We find that small amounts of hydrogen increase
the optical gap up to 2X10(-6) mbar hydrogen pressure, and then the band gap decreases continuously. The absorption tail sharpens by the addition of hydrogen, as
measured by photothermal deflection spectroscopy (PDS) and thus confirms the Raman measurements that suggest that the order in the material increases with
increasing hydrogen content. (C) 2001 Elsevier Science B.V. All rights reserved.

Hüllproteinschichten (S-Layer) sind Protein- oder Glykoproteinschichten auf der Oberfläche vieler Bakterien und Archaea. Sie können als Gitter mit schräger, tetragonaler oder hexagonaler Symmetrie vorliegen. Die Funktion dieser äußersten Zellwandkomponente ist nicht einheitlich und nur teilweise näher untersucht. So können diese zum Beispiel als Schutzhülle, Molekularsieb oder Ionenfalle fungieren oder der Formerhaltung dienen. In neueren Arbeiten konnte gezeigt werden, dass die Hüllproteinschichten verschiedene Metalle binden und in einigen Fällen die Bildung von Nanoclustern ermöglichen. Unter den Aspekten der Wechselwirkungen von Hüllproteinen mit Schwermetallen und der Entwicklung möglicher Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden Hüllproteine von Bakterien untersucht, die von Schwermetall und Radionuklid belasteten Umgebungen isoliert wurden. Dazu wurde ein Hüll-protein eines Bakteriums aus einer Uranabfallhalde isoliert und strukturell sowie molekularbiologisch analysiert.
Im Rahmen der vorgelegten Arbeit wurden mehrere Haldenisolate der Gattung Bacillus hinsichtlich der Existenz von Hüllproteinen untersucht. Dies erfolgte mit Hilfe einer neu entwickelten Methode zum schnellen Nachweis von Hüllproteinen auf Gram-positiven Bakterien. Dabei wird das Peptidoglycan der Zellwand mit Lysozym verdaut und auf diese Weise die Proteinschicht von der Zellwand gelöst. Die freien Schichten können somit im Transmissionselektronenmikroskop oder Atomkraftmikroskop direkt nachgewiesen werden. Es wurde gefunden, dass nur das Isolat Bacillus sphaericus JG-A12 eine Hüllproteinschicht mit tetragonaler Symmetrie und einer Gitterkonstante von 12,5 nm besitzt. Die (135±5) kDa schweren Hüllproteinmonomere sind nicht glykosyliert, weisen aber zwei verschieden stabil gebundene Phosphorspezies auf. Mittels molekularbiologischer Analysen konnten Teile der Hüllproteingene von B. sphaericus JG-A12 (Base 1 bis 1497 des strukturkodierenden Teils des Gens) und des nächst verwandten Referenzstamms B. sphaericus NCTC 9602 (Base 1 bis 579 des strukturellen Teils des Gens) entschlüsselt werden. Beide Hüllproteine besitzen N-terminal drei S-Layer homologe Domänen und weisen in den Aminosäuren 1-182 nur sehr geringe Identitäten zu bereits entschlüsselten Hüllproteinen anderer B. sphaericus Stämme auf. Dem gegenüber ergeben sich hohe Identitäten für die Aminosäuren 183-320 für Hüllproteine mit tetragonaler Symmetrie (Hüllproteine der B. sphaericus Stämme P-1 und CCM 2177) und sehr niedrige für das Hüllprotein mit schräger Symmetrie (Hüllprotein von B. sphaericus WHO 2362).

Im Hinblick auf katalytische Anwendungen oder der Entwicklung von Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden die Wechselwirkungen von Hüllproteinen mit verschiedenen Metallen untersucht. Es konnten direkte Wechselwirkungen von Palladium, Platin und Uran mit den Hüllproteinen von B. sphaericus JG-A12 und NCTC 9602 nachgewiesen werden. Die Ergebnisse zeigen für beide Proteine eine Komplexierung von Platin über CO- und NH-Gruppen der Peptidbindungen und über COOH- und OH-Gruppen. Das Hüllprotein von B. sphaericus JG-A12 komplexiert Palladium über NH-Gruppen der Peptidbindung und COOH-Gruppen, während das von B. sphaericus NCTC 9602 Palladium sowohl über CO-Gruppen der Peptidbindungen als auch über COOH- und OH-Gruppen bindet. Die Komplexierung von Uran erfolgt vorrangig über NH-Gruppen der Peptidbindungen aber auch über OH- sowie zwei verschiedene PO4-Gruppen. Um eine Anwendung der metallbindenden Eigenschaften von Hüllproteinen im Rahmen von Bioremediationsprozessen zu ermöglichen, wurden diese mittels Sol-Gel-Technik in einer SiO2-Matrix immobilisiert und die Sorption und Desorption von Uran und Kupfer untersucht. Zum Vergleich wurden intakte Zellen und Sporen immobilisiert und in die Untersuchungen mit einbezogen. Die biologisierten Keramiken (Biocere) binden 2,7-42fach mehr Uran und Kupfer als andere zur Sanierun...

Energiereiche Neutronenstrahlung verursacht in Materialien Schädigungen, die zum Verlust ihrer mechanischen Festigkeit führen. Ein solcher Effekt ist die Neutronenversprödung. Für Komponenten, die sich innerhalb bzw. nahe des Kerns eines Spaltreaktors befinden, ist sie der wichtigste Schädigungsmechanismus. Für den Druckbehälter ist sie von besonderer Sicherheitsrelevanz. Da sich die Schädigung mit fortlaufender Bestrahlung akkumuliert, ergibt sich aus Sicherheitsgründen für eine Komponente eine maximal zulässige Strahlungsfluenz, der sie ausgesetzt werden darf. Bei vielen Druckwasserreaktoren ist der Materialzustand des Druckbehälters sogar entscheidend für die zulässige Betriebsdauer des Reaktors. Daher ist einerseits die Monitorierung der Strahlungsbelastung für sicherheitsrelevante Komponenten mit Hilfe geeigneter Messungen und Berechnungen eine notwendige Voraussetzung für den sicheren Betrieb eines Kernreaktors und andererseits die Entwicklung und Verifikation solcher Mess- und Berechnungsmethoden eine wichtige Aufgabe der Reaktorsicherheitsforschung. Die möglichst zuverlässige Bestimmung der Strahlungsbelastung für kernnahe Komponenten, darunter insbesondere des Druckbehälters, zu ermöglichen, ist das Ziel des Fachgebiets "Reaktordosimetrie". Seine Bearbeitung auf hohem wissenschaftlich-technischen Niveau ist daher eine notwendige Voraussetzung für zuverlässige Integritätsbewertung und Gewährleistung von Komponentensicherheit.

Nach dem Zusammenbruch des Ostblocks ist die Sicherheitsproblematik der Druckbehälter der russischen Kernreaktoren vom Typ WWER weltweit ins Blickfeld der Öffentlichkeit gerückt und zum Gegenstand zahlreicher Forschungsprojekte geworden. Da in diesem Falle die Strahlenschädigung im Vergleich zu anderen Effekten wesentlich größer ist, hat insbesondere die Reaktordosimetrie dadurch neue Impulse erfahren. Mit der Neugründung des Forschungszentrums Rossendorf aus dem ehemaligen ZfK Rossendorf wurde auch ein Teil der reaktordosimetrischen Arbeiten zu WWER-Reaktoren übernommen und im Institut für Sicherheitsforschung parallel zur entsprechenden Materialforschung fortgeführt. Bisher wurden hier die wichtigsten Teilgebiete bearbeitet: Fluenzmessung, Fluenzberechnung und Spektrumsjustierung. Im Vortrag werden der erreichte Stand dargelegt, dieser mit dem internationalen Niveau verglichen und Ansätze für Weiterentwicklungen aufgezeigt.

Early evidence that small technetium compounds may be subject to active transport processes was provided by the historical serependipitous finding that pertechnetate was handled by the sodium-iodide symporter in the thyroid gland. The pertechnetate ion can mimic the iodide ion, despite its different nature and geometry.
Starting from this observation ^99mTc radiotracers are designed for probing and imaging a distinct biochemical reaction of diagnostic relevance. Such biochemical reactions are transmembrane processes, binding reactions, enzymatic conversions, possibly redox reactions, etc., and key proteins or enzymes are the targets of the ^99mTc diagnostic agents. "Bioactivity" is therefore required in the sense of the ^99mTc species being able to participate in the biochemical reaction of interest, being bound or processed.
Keeping the artificiality of technetium in the human body in mind, the feasibility of biochemical Tc-99m probes can only be based on imperfection of the target specificity, on the tolerance of the target molecule towards a substrate mimic that accidentally fits the target molecule to some extent, despite its different chemical nature. This will be examplified by the development of ^99mTc ligands for brain receptors.
The possibility of using biochemical ^99mTc probes for various CNS receptors is due to the tolerance of the target molecules towards metal-based mimics. As the high in-vitro affinities to various neuroreceptors in the nanomolar and subnanomolar range indicate, molecular recognition of complex technetium molecules has become possible.
However, one main issue in developing CNS receptor imaging agents remains the very low or totally absent brain uptake. After two decades of research into brain ^99mTc perfusion agents it has now become feasible for certain technetium complexes to cross the blood-brain barrier. In contrast, a suitable combination of a high receptor affinity with a sufficient brain uptake was not achieved. Systematic studies of model technetium compounds with various logP and pKa values provided rules for selected homologous series of complexes but did not really help to tackle the problem. Since a wide variety of chemically diverse compounds, among them lipophilic cations such as ^99mTc MIBI, ^99mTc tetrofosmin or Q-series compounds, may be actively transported out of the cell by P-glycoprotein, it might also affect the transport of potentially receptor-binding ^99mTc agents.

To conclude, approaches to specific small technetium radiopharmaceutical tracers have not changed much in recent years. From a coordination chemistry point of view, the design of new ^99mTc radiopharmaceuticals starts conceptually with the modification of the coordination environment around the metal with a variety of chelators. Diversity of the chelate unit is needed, and considerable research has consequently been devoted to designing improved and new chelate types, resulting in a flourishing technetium chemistry. New impetus has come in particular from the progress made in technetium(I) chemistry.
Although this knowledge explosion in the technetium chemistry has been translated into targeted radiopharmaceutical research activity the number of newly launched Tc-99m radiopharmaceuticals is stagnant, at least in a short-term perspective. The development of biochemically specific, small technetium and rhenium complexes remains therefore a challenging, rewarding and often frustrating activity.

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no abstract delivered from author

Inhalt

• Material: Halbleiter-Heterostrukturen aus SiC in Si, Diamant in SiC, SiC in Diamant
• Ionenstrahlsynthese: Ionenverteilung im Material, Strahlenschäden, Temperatur-behandlung bei und nach Implantation
• Bedeutung der Synchrotronstrahlung für die Materialforschung, Rossendorfer Beamline an der ESRF Grenoble
• Materialcharakterisierung wie Phasen-bildung, Kristallitgröße und -orientierung, Gitterdeformation in Matrix und Kristallit mittels diverser Röntgenmethoden
• Ausblick: simultane Doppelimplantation

CFD codes are more and more used for practical applications as the design and optimization of technical facilities, e.g. in process industry or in nuclear power plants. For most cases this limited to single phase flows. To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with high reso-lution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary condi-tions. Local bubble size distributions are calculated from the data. The measure-ments were done in different distances from the gas injection device. As a result the development of bubble size distributions and the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe.

Oxidized LDL (oxLDL) is a key mediator in atherogenesis and a marker of coronary artery disease (CAD). Type 2 diabetes is associated with excessive cardiovascular morbidity and mortality. Because atherogenesis starts before diabetes is diagnosed, we investigated whether circulating oxLDL levels are increased in impaired glucose tolerance (IGT). OxLDL levels were measured in 376 subjects with normal glucose tolerance (NGT), 113 patients with IGT, and 54 patients with newly diagnosed type 2 diabetes. After correction for age and BMI, serum levels of oxLDL were significantly increased in IGT versus NGT subjects (P = 0.002). OxLDL levels were not associated with the following parameters of the oxidative/antioxidative balance in the blood: total antioxidant capacity, urate-to-allantoin ratio, and circulating phagocyte oxygenation activity. In stepwise multivariate analysis, LDL cholesterol (P < 0.0005) and triglycerides (P < 0.0005) were the strongest predictors of circulating oxLDL levels, followed by HDL cholesterol (P = 0.003), 2-h postchallenge C-peptide (P = 0.011), fasting free fatty acids (P = 0.013), and serum paraoxonase activity (P = 0.035). The strong correlation of oxLDL with LDL cholesterol and triglycerides indicates that LDL oxidation in IGT is preferentially associated with dyslipidemia. OxLDL increase may explain the high atherogenic potency of dyslipidemia in the prediabetic

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
A more detailed analysis shows that several stages should be considered corresponding to different dominating processes on very different time scales. For investigation of the film growth in the short time impact stage molecular dynamics was used. For this purpose the empirical interaction potential of Brenner was modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) was quantitatively analysed in dependence on particle energy and temperature.
The results of the impact stage represent the input data for the long time diffusion stage. Based on continuum mechanics a simplified model for the further film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

Range distributions of carbon ions deposited onto tetrahedral amorphous carbon films at kinetic energies between 22 eV and 692 eV are measured utilizing high-resolution elastic recoil detection. These data are compared to range calculations based on binary collision approximation as well as to classical molecular dynamics simulations. Asymmetric range profiles, differences in mean ion ranges and increased range straggling compared to theories are attributed due to self diffusion during thermal spike and have to be considered in subplantation growth models.

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
To understand the film growth on a quantitative level molecular dynamics has been used. For this purpose the empirical interaction potential of Brenner has been modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) has been quantitatively analyzed in dependence on particle energy and temperature.
Based on these fundamental studies a simplified model for the film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

The corrosion of metals is associated both with a release of ions and changes in optical surface properties. In this study these two effects were correlated by a potentiodynamic corrosion test and in situ probing of the surface by ellipsometry. The studies were carried out with stainless steel AISI 304 and 316 in phosphate buffered saline (PBS) and in Dulbecco's Modified Minimal Essential Medium (DMEM) at pH 7.4. In both media 304 steel is more susceptible to corrosion than 316 grade. The 316 steel shows higher corrosion potential and higher corrosion current density in PBS than in DMEM, for 304 steel this behavior is vice versa. Ellipsometry demonstrated a higher sensitivity than potentiodynamics to surface modification in the cathodic area. In DMEM the removal of a surface layer at negative voltage and a further repassivation with increasing voltage was characteristic. In PBS a surface layer started to grow immediately. X-ray photoelectron spectra of this layer formed in PBS are consistent with iron phosphate. Its formation is inhibited in DMEM; the presence of aminoacids is discussed as the reason.

The morphological evolution of nanostructures on semiconductor surfaces eroded by low-energy ion beams has gained particular interest recently as a possible way to generate regular, ordered, and highly dense quantum dots. Generally, the erosion by ion beams increases the surface roughness, which under certain sputter conditions can turn to periodic surface structures. At normal incidence of the ion beam hexagonally arranged dot patterns appear on the eroded surface. The diameter of these structures is in the range of 15 - 80 nm depending on ion energy with a density up to 2x10^11cm^-2.
After an initial stage of irradiation the temporal evolution of the dot pattern can be described by a stochastic continuum equation. In the case of crystalline semiconductor surfaces rapid amorphization and variation in stoichiometry takes place. As the erosion process proceeds nanoscale dot structures appear at the surface, which are remarkable well ordered and grow up to an aspect ratio of nearly unity. We present the temporal evolution of dot pattern formation on GaSb (100) surfaces during Ar+ ion sputtering. The characteristic length of the dot pattern is determined as a function of ion energy, ion current density, and sample temperature.

Ion beam deposition of carbon films was studied by molecular-dynamics simulations. Using an analytic hydrocarbon potential of Brenner with an increased C-C interaction cutoff value, deposition of films with a thickness of up to 10 nm was simulated for ion energies E_ion =10-80 eV, and for substrate temperatures T_s ranging from 100 to 900 K. The bulk properties of the computed tetrahedral amorphous carbon (ta-C) films as well as structure and roughness of their sp² -rich surface layers agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp³ fraction in the films increases with ion energy, resulting in a highly sp³ -bonded ta-C with a high compressive stress for E_ion >30 eV. This trend remains also at room temperature, however with lower sp³ content and stress.
In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as T_s exceeds a critical temperature T_c . The calculated transition temperature T_c is a bit too low (T_c ~100 ^oC for E_ion =40 eV). For the ion energies E_ion ≤ 80 eV, the incidence atom is predicted to come to rest in the sp² -rich surface layer. A time-resolved analysis of the film formation shows that atom subplantation leads generally to a highly tetrahedral structure, but above T_c the kinetic energy of the atoms is sufficiently large to overcome the barrier in cohesive energy between ta-C and the more stable graphite-like films.

The complexation of uranium(VI) by humic and fulvic acids was studied to obtain information on the binding of uranium(VI) onto functional groups of humic substances. For this, various natural and synthetic humic acids were chemically modified resulting in humic acids with blocked phenolic OH groups. Both from the original and from the modified humic substances, solid uranyl humate complexes were prepared at pH 2. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to study the chemical modification process of humic substances, to study the structure of uranyl humate complexes and to evaluate the effect of individual functional groups of humic substances (carboxylic and phenolic OH groups) on the complexation of uranyl ions. The results confirmed the predominant blocking of phenolic OH groups in the modified humic acids. These modified humic acids are suitable model substances to study the role of phenolic OH groups of humic acids in dependence on pH. By EXAFS spectroscopy, identical structural parameters were determined for all uranyl humates. Axial U-O bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of humic acids did not change the near-neighbor surrounding of uranium(VI) in uranyl humate complexes. Thus, the results confirmed that predominantly humic acid carboxylate groups are responsible for binding of uranyl ions and that the influence of phenolic OH groups is insignificant under the applied experimental conditions. The carboxylate groups are monodentate coordinated to uranyl ions.

The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar.
The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.

A combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X -ray (EDX) was used to conduct a molecular and atomic analysis of the uranium complexes formed by A. ferrooxidans. The results demonstrated that this bacterium accumulates uranium as phosphate compounds. We hypothesize that the poly P-bodies of A. ferrooxidans may play a role in detoxification of those part of uranium which is uptaken by the cells.

BACKGROUND: Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade. METHODS: Titanium oxide films were produced by metal plasma deposition and implantation in form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the electronic band gap of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples. RESULTS: The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces. CONCLUSION: Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

This work reports the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: (i) conventional method of doping by implanting with N into an ion beam synthesized SiC layer and (ii) a novel method based on pre-doping (with N and P) of the Si wafers before the ion beam synthesis of SiC. For the N implantation the electrical data show a p-type overcompensation of the SiC layers for both doping methods used. The structural (XRD) and in-depth (SIMS, Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N ion implantation damage, and therefore, the need for further optimization of their thermal processing. In contrast, the P-doped SiC layers always show n-type conductivity. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the undoped material. Our electrical data, together with the absence of additional stress related to P-implant suggest that this technique could be suitable to avoid effects related to the ion implantation damage in the SiC lattice, although the electrical activation of P in the SiC is about one order of magnitude lower than in Si.

This work reports preliminary data on the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: i) doping by ion implantation (with N) of ion beam synthesized SiC layers and ii) ion beam synthesis of SiC in previously doped (with P) Si wafers. In the first case, the electrical data show a p-type overcompensation of the SiC layer in the range of temperatures between -50°C and 125 °C. The structural (XRD) and in-depth (SIMS; Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N-ion implantation damage, and therefore the need for further optimization of their thermal processing. In contrast, the p-doped SiC layers always show n-type doping. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the not doped material. Electrical activation of P in the SiC lattice is about one order of magnitude lower than in Si. These data constitute, to our knowledge, the first results reported on the doping of ion beam synthesized SiC layers.

Benchmark calculations for the validation of the coupled neutron kinetics/thermohydraulic code complex DYN3D-ATHLET are described. Two benchmark problems concerning hypothetical accident scenarios with leaks in the steam system for a VVER-440 type reactor and the TMI-1 PWR have been solved. The first benchmark task has been defined by FZR in the frame of the international association "Atomic Energy Research" (AER), the second exercise has been organised under the auspices of the OECD. While in the first benchmark the break of the main steam collector in the sub-critical hot zero power state of the reactor was considered, the break of one of the two main steam lines at full reactor power was assumed in the OECD benchmark. Therefore, in this exercise the mixing of the coolant from the intact and the defect loops had to be considered, while in the AER benchmark the steam collector break causes a homogeneous overcooling of the primary circuit. In the AER benchmark, each participant had to use its own macroscopic cross section libraries. In the OECD benchmark, the cross sections were given in the benchmark definition. The main task of both benchmark problems was to analyse the re-criticality of the scrammed reactor due to the overcooling.
For both benchmark problems, a good agreement of the DYN3D-ATHLET solution with the results of other codes was achieved. Differences in the time of re-criticality and the height of the power peak between various solutions of the AER benchmark can be explained by the use of different cross section data. Significant differences in the thermohydraulic parameters (coolant temperature, pressure) occurred only at the late stage of the transient during the emergency injection of highly borated water. In the OECD benchmark, a broader scattering of the thermohydraulic results can be observed, while a good agreement between the various 3D reactor core calculations with given thermohydraulic boundary conditions was achieved. Reasons for the differences in the thermohydraulics were assumed in the difficult modelling of the vertical once-through steam generator with steam superheating.
Sensitivity analyses which considered the influence of the nodalisation and the impact of the coolant mixing model were performed for the DYN3D-ATHLET solution of the OECD benchmark. The solution of the benchmarks essentially contributed to the qualification of the code complex DYN3D-ATHLET as an advanced tool for the accident analysis for both VVER type reactors and Western PWRs.

VALCO is an EU FP5 project on transient analysis code validation for VVER type reactors that continues the work of the former EU Phare project SRR1/95. Twelve organisations from nine East and West European countries are participating. For the validation of coupled neutronic / thermal-hydraulic codes that are used in VVER safety analyses, five measured transients from different VVER-440 and VVER-1000 plants have been documented. Two of them have been chosen for validation calculations. First results of an ATHLET / DYN3D calculations for a MCP trip measured in the Kozloduy-6 VVER-1000 are presented. Uncertainty analysis applying the SUSA methodology developed at GRS to coupled-code calculations for VVER will be performed. To validate the stand-alone three-dimensional neutronic codes together with the applied two-group diffusion parameters independently from thermohydraulic feedback, the analysis of measurements in the V-1000 zero-power facility (KI Moscow), which is a full-scale VVER-1000 mock-up, is going to be performed. Preliminary results of DYN3D steady-state calculations using a HELIOS two-group data library and albedo coefficients calculated by the transport code MARIKO are compared to measurement data.

Thin films of semiconducting iron disilicide (ß-FeSi2)with up to 8 at.% Cr addition grown on Si(001) and Si(111) substrates were studied by spectroscopic ellipsometry as well as transmission and reflection measurements at room temperature. The dielectric function was deduced in the interband spectral range. In molecular beam epitaxy (MBE) preparation part of the Fe atoms were substituted by Cr during deposition. For a low Cr amount in the doping range up to about 0.4 at.%, Cr was found to modify epitaxial growth on Si(111) substrates with a change in dominating ß-FeSi2 grain orientation. Higher amounts of Cr lead to the precipitation of CrSi2, which was detected optically and confirmed by x-ray diffraction measurements and a deterioration of film morphology. Furthermore, ß-FeSi2 thin films were implanted with Cr and subsequently annealed at varios temperatures. In these samples also CrSi2 was detected. The results suggest that it is impossible to produce ß-(Fe(1-x)Cr(x))Si2 alloys by MBE or ion implantation.

Diamondlike amorphous carbon (DLC) is a transparent hard material approaching crystalline diamond in hardness and elastic modulus. The main issue restricting applications of this very promising material is a high compressive stress in DLC films after growth. I present recent results of atomic scale calculations of growth and mechanical properties of DLC films performed in collaboration with H.-U. Jaeger. The following topics are discussed:

- the nature of intrinsic stresses in DLC films;
- the dependence on the intrinsic stresses on the film deposition parameters;
- the effect of the intrinsic stresses on the second-order elastic constants of amorphous carbon.

The atomic models of DLC films are prepared by direct molecular dynamics simulation of ion-beam deposition. Similar to real as-deposited films, the simulated films have a high content of tetrahedrally coordinated atoms and large intrinsic compressive stresses in the region of steady-state growth. The stress in the region of steady-state growth is calculated as an average of atomic-level stresses derived from an empirical interatomic potential. The origin of the intrinsic stress in DLC films is discussed on the basis of the structural changes due to thermal annealing simulated by molecular dynamics method. We propose that the high stress in DLC films can be
related to local defects in amorphous carbon networks. The dependence of the second-order elastic contants of amorphous carbon on the intrinsic stress is examined by the method of homogeneous deformation. We nonlinear effects are shown to become appreciable at the stress values typical of as-deposited DLC films.

Der Vortrag berichtete über unsere Simulationen zur Ionenstrahlabscheidung von
Diamant-ähnlichen Kohlenstoffschichten. Zuerst wurden die typischen Resultate
einer Rechnung vorgestellt. Danach wurden der sp³-Gehalt der Filme,
ihre Dichte, die Bindungsenergie der Atome und die Struktur der Graphit-ähnlichen Filmoberfläche erläutert.

Three different methods for measuring the depth distribution of dopants in 4H-SiC have been investigated: (1) Spreading Resistance Profiling (SRP), (2) Scanning Capacitance Microscopy(SCM) and (3) Scanning Electron Microscopy (SEM). The investigated samples included p- and n-type epitaxial layers grown by vapor phase deposition with doping concentrations of 10E16 - 10E20 cm-3. Also p+n implanted profiles using a combination of Al and B multi-energy implantation were studied. All techniques were able to provide doping profiles qualitatively corresponding to Secondary Ion Mass Spectrometry (SIMS) data. The SRP results suggest a lower limit of the p-doping concentration below which the ohmic contact between the probe tip and sample become more Schottky-like. The magnitude of the SCM signal corresponds well to the chemical doping profile except in the depleted region surrounding the metallurgical junction of the p+n structure.

In einem mehrjährigen umfangreichen Bestrahlungsprogramm wurden in den Bestrahlungskanälen des Reaktors WWER-2 des KKW Rheinsberg Druckbehälterstahlproben bestrahlt. Das Programm diente der Erweiterung der Datenbasis zur Bewertung der Strahlenversprödung von Reaktordruckbehälterstählen. Zur Ermittlung der Neutronenbelastung wurden die Bestrahlungskapseln mit Neutronenaktivierungsdetektoren bestückt. Der Bericht enthält die Beschreibung des Typs, des Aufbaues und der Zusammensetzung der Neutronenfluenzmonitore, ihre Anordnung im jeweiligen Experiment, die Auswerteprozedur nach der Bestrahlung und gibt eine zusammenfassende Übersicht über die gemessenen und spektrumsjustierten Neutronenfluenzen für alle 8 Einzelexperimente des Bestrahlungsprogrammes Rheinsberg II. Die Ergebnisse der neutronendosimetrischen Messungen sind konsistent mit den Ergebnissen der Neutronenfeldrechnungen und ergeben in Verbindung mit diesen zuverlässigen Daten über die Neutronenbelastung der in den Bestrahlungsexperimenten neutronen-exponierten Materialproben.

A mass selected focused ion beam is employed for the fabrication of plasmonic structures applying different techniques. So the local implantation of equidistant gold-dots of some ten nm diameter in a silicon or SiO2 target will be studied. Also the local growth of Au-dots after a FIB pre-treatment is a promising approach due to the low adhesion of Au on Si and SiO2 surfaces. Dots or columns can also be achieved by sputtering small holes in a thin film and filling them with noble metals. A new approach is the local ion beam synthesis of CoSi2 nano-structures after cobalt-FIB implantation and annealing. An additional possibility is the growth of metal structures in a FIB aided CVD process using a certain precursor metal-organic gas.

An alternative approach for the fabrication of SiCOI material based on ion beam synthesis technique IBS is presented. Combining IBS with wafer bonding, high crystalline quality ß-SiC layers with low residual strain, have been successfully transferred onto oxidized Si wafers, obtaining SiCOI structure with abrupt SiC/SiO2 interfaces and low surface roughness.

Combining He ion irradiation and thermal mobility below 600K, we both trigger and control the transformation from chemical disorder to order in thin films of an intermetallic ferromagnet (FePd). Kinetic Monte Carlo simulations show how the initial directional short range order determines order propagation. Magnetic ordering perpendicular to the film plane was achieved, promoting the initially weak magnetic anisotropy to the highest values known for FePd films. This post-growth treatment should find applications in ultrahigh density magnetic recording.

Many recent conferences on ion beam processing of materials have concentrated on process optimisation, with comparatively less effort on understanding basic science features. It seemed timely to reverse this trend, and focus on ion beams as a tool for probing the basic materials processes and properties or for exploring the more fundamental aspects of nonequilibrium modifications induced by irradiation.

Symposium O, "Ion Beam Synthesis and Processing of Advanced Materials",was held November 27-29 at the 2000 MRS Fall Meeting in Boston, Massachusetts, USA. 116 papers were presented in fourteen sessions including two poster sessions. The sessions were well attended and the discussion were lively.

Auf der Basis von Nanostrukturen gibt es völlig neue Funktionsprinzipien und
Bauelementekonzeptionen für die Elektronik und Optik. Es wird gezeigt, dass
der Ionenstrahl als etabliertes Werkzeug der Mikroelektronik auch bei der
Züchtung (Ionenstrahlsynthese) und Zähmung (Eigenschaftsänderung)
von Nanostrukturen ein technologiefreundliches Verfahren ist. Es müssen
Selbstorganisationsphänomene verstanden und eingesetzt werden, die bei der
Prozeßführung weitab vom thermodynamischen Gleichgewicht auftreten.
Hierzu gehören die inverse Ostwald-Reifung unter Ionenbestrahlung, die Ordnung von Präzipitaten bei der Phasenseparation und die Pearling-Instabilität. Zwei Anwendungen werden vorgestellt: Die Entwicklung eines nichtflüchtigen Halbleiterspeichers (nvRAM) und die Lichtleitung in Goldclusterketten für die Nanooptik (Plasmonics).

The control of the MOSFET channel by nanoclusters within the gate oxide, which are charged/decharged due to direct e--tunneling, provides a conceptually very simple non-volatile memory. The development of reliable processes for the production of the required nanocrystals on an industrial scale is a big challenge to current research. The two processes being favored at present are the self-organization of nanocluster-delta-layers after ion implantation [1] and the deposition of Si aerosols [2]. Here, we present an alternative process taking advantage of the well-known self-assembling of Ge quantum dots on (001)Si [3,4] in combination with chemical reduction of GeO2 by Si during thermal treatment [5]. Using process simulations it will be studied, how, in comparison to pure thermal treatment, ion-irradiation induced detachment of Si monomeres from the Si/SiO2 interface accelerates the Ge precipitation due to the GeO2+Si --> SiO2+Ge reaction. For our study it was assumed that self-assembled Ge nanoclusters on Si [3,4] were covered by a Si layer, and, finally, oxidized under special conditions [5] which suppresses Ge segregation. The resulting thin gate oxide with embedded GeO2 clusters is the starting point of our kinetic Monte-Carlo simulations. In an fcc-cell of about 256000 lattice points having periodic boundary conditions in the interface plane, Ising-model-like interactions in the two-component system (Si and Ge) and the reaction GeO2+Si-->SiO2+Ge are taken into account. Additionally, according to ion beam mixing estimated by TRIM calculations, atomic displacements of Si bulk and nanocluster atoms have been considered.
[1] K.H.Heinig, B.Schmidt,.M.Strobel, H.Bernas, Mat.Res.Soc.Proc. v.650(2001).
[2] H. Atwater, J.W. De Blauwe et al., Mat.Res.Soc.Proc. v.638(2001).
[3] F. Jensen, J.W. Petersen, S.Y. Shiryaev, A.N. Larsen, Nanotechn. 7, 117 (1996).
[4] O.Pchelyakov, Y.Bolkhovityanov, A.Dvurechenskii, Thin Solid Films 367, 75 (2000).
[5] Y.-C.King, T.-J.King, C.Hu, Int.Electron Dev. Meeting Technical Digest (1998), 115.

The control of the MOSFET channel by nanoclusters within the gate oxide, which are charged/decharged due to direct e--tunneling, provides a conceptually very simple non-volatile memory. The development of reliable processes for the production of the required nanocrystals on an industrial scale is a big challenge to current research. The two processes being favored at present are the self-organization of nanocluster-delta-layers after ion implantation [1] and the deposition of Si aerosols [2]. Here, we present an alternative process taking advantage of the well-known self-assembling of Ge quantum dots on (001)Si [3,4] in combination with chemical reduction of GeO2 by Si during thermal treatment [5]. Using process simulations it will be studied, how, in comparison to pure thermal treatment, ion-irradiation induced detachment of Si monomeres from the Si/SiO2 interface accelerates the Ge precipitation due to the GeO2+Si --> SiO2+Ge reaction. For our study it was assumed that self-assembled Ge nanoclusters on Si [3,4] were covered by a Si layer, and, finally, oxidized under special conditions [5] which suppresses Ge segregation. The resulting thin gate oxide with embedded GeO2 clusters is the starting point of our kinetic Monte-Carlo simulations. In an fcc-cell of about 256000 lattice points having periodic boundary conditions in the interface plane, Ising-model-like interactions in the two-component system (Si and Ge) and the reaction GeO2+Si-->SiO2+Ge are taken into account. Additionally, according to ion beam mixing estimated by TRIM calculations, atomic displacements of Si bulk and nanocluster atoms have been considered.
[1] K.H.Heinig, B.Schmidt,.M.Strobel, H.Bernas, Mat.Res.Soc.Proc. v.650(2001).
[2] H. Atwater, J.W. De Blauwe et al., Mat.Res.Soc.Proc. v.638(2001).
[3] F. Jensen, J.W. Petersen, S.Y. Shiryaev, A.N. Larsen, Nanotechn. 7, 117 (1996).
[4] O.Pchelyakov, Y.Bolkhovityanov, A.Dvurechenskii, Thin Solid Films 367, 75 (2000).
[5] Y.-C.King, T.-J.King, C.Hu, Int.Electron Dev. Meeting Technical Digest (1998), 115.

Nanoclusters (N) can be generated by ion implantation of impurity atoms into a host matrix and subsequent phase separation of the impurity phase from the matrix during annealing. This is a CMOS technology compatible process, which has great potential for applications. However, a serious problem arises: The NCs have a broad size distribution, which obscures the size dependent characteristics of the NCs.
Here, we show that irradiation of NCs with high-energy ions can be used to overcome this problem. During irradiation, the collisional mixing at the NC-matrix interfaces competes with phase separation. A negative interface tension can be the consequence, which can only be understood in terms of non-equilibrium thermodynamics. The negative interface tension leads to unexpected results: The system will evolve towards a state of maximal surface area!! Thus, a flat interface
becomes instable. Here, we focus on the Gibbs-Thomson relation with a negative interface tension, where we find an increasing solute concentration with increasing NC size. This is inverse to equilibrium behavior. Consequently, we find inverse Ostwald-ripening, e.g. small NCs grow at the expense of large ones. This can be used for the fabrication of monodisperse NCs. These theoretical predictions have been verified by kinetic MC simulations and by ion irradiation of Au NCs in a SiO2 matrix.

no abstract delivered frm author

We aim at a deeper understanding of how thermodynamic systems that have been driven far-from-equilibrium by ion implantation or irradiation may either relax towards equilibrium (in which case self-organisation phenomena are observed frequently), or - alternatively - be driven into stationary nonequilibrium states (where dissipative structures may develop). The far-from-equilibrium states having a high supersaturation and/or specific interface energy relax by nucleation, growth and coarsening. The stationary states are driven by irradiation damage (dpa/sec) and shows new phenomena like inverse Ostwald ripening. Kinetic 3D lattice Monte Carlo simulations were applied succesfully to predict routes of far-from-equilibrium processing of tailored quantum dots and wires for electronic and photonic applications.

Metal and semiconductor nanostructures embedded in insulators, in particular in SiO2, attract at present much interest due to their potential application in microelectronics (nanocluster memories), optoelectronics (luminescence from Si nanocrystals) and photonics (plasmonic devices using Au nanoclusters). The nanostructures can be synthesized by ion implantation and modified by ion irradiation. Thereby, radiation effects in the matrix as well as in the nanostructures induce self-organisation phenomena, which might allow to control, e.g., the spatial and size distribution of nanoclusters.
Two different regimes of self-organization will be discussed: (i) Relaxation regime: Ion implantation of impurity atoms may produce extremely supersaturated solid solutions. During subsequent annealing this far-from-equilibrium state relaxes towards equilibrium by phase separation (nucleation, growth) and minimization of interface energy (Ostwald ripening, coalescence). Self-organization phenomena (e.g. pattern formation during phase separation, Rayleigh or pearling instability during interface minimization) have been found. (ii) Driven system: Interfaces or compounds like SiO2 can be driven into a steady state far from equilibrium by ion irradiation. The steady state is established by a competition between collisional mixing, diffusion and re-formation of the compound. For driven systems a theoretical study and atomistic computer simulations of radiation effects like the nanocluster d-layer formation and ''inverse'' Ostwald ripening will be presented.

no abstract delivered from author

The evolution of diffusively interacting nanoclusters is investigated by combined atomistic (kinetic lattice Monte Carlo method based on the nearest-neighbor Ising model) and mean-field (numerical integration of the governing reaction-diffusion equations) simulations. By expressing Monte Carlo parameters in terms of macroscopic thermodynamic quantities a well-defined interface between both methods is derived. Based on extensive Monte Carlo studies of the Gibbs-Thomson equation an explicit expression for the intrinsic capillary length is presented. Starting with
high-temperature quenches, the evolution of nanoclusters is first studied by the atomistic model. The observed transient dynamics of coarsening is explained uniquely on the basis of the ratio of the capillary length to the mean cluster size. Using input data from the atomistic model, Ostwald ripening is also studied in parallel with the mean-field model. In a detailed study, the similarities and differences of both approaches are discussed and explained in terms of their statistical and deterministic natures. It is demonstrated that in contrast to the commonly applied linearized version of the Gibbs-Thomson relation in the mean-field approach only the use of the full exponential form provides a reasonable matching with the atomistic model.

During annealing at 950°C in an oxidizing ambient, the redistribution of Ge in Ge+-implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM. Sputtering depth profiling in conjunction with the X-ray photoelectron spectroscopy (XPS) analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.

Ion nitriding of Al has been performed by a nitrogen reactive ion beam using a hot filament ion source. The N incorporation has been determined at different beam voltage from 0.4 kV to 2.4 kV with an ion current density of 0.2 mA/cm2, and a substrate temperature of 350°C. For this purpose, the beam has been characterised in terms of ion flux, ion composition and energy distribution using an energy selective mass spectrometer and a Faraday cup. From the beam parameters, N loss due to sputtering and backscattering has been calculated as a function of the ion energy using dynamic binary collision computer simulations. The total amount of incorporated N measured by Nuclear Reaction Analysis (NRA) is consistent with the incident N fluence and the N loss obtained from the simulation. A discrepancy is observed for a beam voltage lower than 0.8 kV due to the stationary surface oxide layer reducing the rate of nitrogen incorporation during ion nitriding of Al.

Die Strahlenversprödung von Druckbehältermaterialien heutiger Kernreaktoren, die durch die anliegenden Neutronen- und Gammafelder verursacht wird, ist meistens durch die Neutronen dominiert. Durch experimentelle Befunde ist aber belegt, dass unter bestimmten Umständen die Gammastrahlung nicht zu vernachlässigen ist und sogar den Hauptbeitrag liefern kann. Die Materialforschung konnte bis heute nicht klären, mit welcher Effektivität beide Strahlungsarten zur Versprödung beitragen.
Im Bericht sind die wesentlichen Ergebnisse, die im Vorhaben Nr. 150 1221 der Reaktorsicherheitsforschung erziellt wurden, dargelegt. Es hatte das Ziel, den aktuellen Kenntnisstand der Materialforschung aufzuarbeiten und auf dessen Grundlage für jeweils zwei russische und deutsche Reaktortypen den Einfluss der Gammastrahlung auf die Versprödung ihrer Druckbehälter abzuschätzen. Die notwendigen Neutronen/Gamma-Fluenzberechnungen wurden mit den SN-Programmen DORT/ANISN unter Verwendung der Gruppendatenbibliothek
BUGGLE-96T und mit dem Monte-Carlo-Code MCNP4C mit den Kerndaten aus der Bibliothek ENDF/B-VI Rev. 3 durchgeführt. Beide Programm- und Datenpakete stellen den heutigen Entwicklungsstand der reaktordosimetrischen Fluenzberechnungen dar. Aus den erzielten Ergebnissen wurden die Konsequenzen für die Bewertung der Druckbehälterversprödungen abgeleitet, Fehlerbetrachtungen dazu durchgeführt und der Einfluss der Gammastrahlung auf reaktordosimetrische Messungen ausgewiesen.

Phase analysis on ion treated surfaces by conversion electron
Mössbauer spectroscopy